The present invention relates to representing and animating paint strokes.
A paint stroke is defined in two dimensions: position and time. In the position dimension, the stroke is defined by a stroke path that extends from a start position to an end position. In the time dimension, the stroke is defined by a timing that reflects the actual time it takes to draw or compose the stroke. This timing will be referred to as composition time.
The appearance of the paint stroke is defined by values for one or more stroke parameters. Stroke parameters can include, for example, thickness, feather, and hardness. The values for the stroke parameters can vary along the stroke path. For example, a stroke thickness parameter can have a smaller value at a first position along the stroke path and a larger value at a second position further along the stroke path; these values can be used to define a stroke that becomes thicker between the first and second positions along the stroke path.
In this specification, animating a paint stroke refers to displaying the paint stroke such that its appearance changes over time. This effect can be produced by creating multiple instances of the paint stroke, each instance corresponding to a different appearance of the stroke, and then displaying each instance one after another in time. The timing of when each instance is displayed will be referred to as the animation time.